Whole Skin Locomotion (WSL) is an amoeba inspired locomotion mechanism for mobile robots in which an elongated torus turns itself inside out in a single continuous motion. Since the entire surface is used as a traction surface, WSL has the potential to traverse highly unstructured terrain, and when filled with fluid with an elastic membrane skin, it has the potential to squeeze through holes smaller than its nominal diameter. Previous work has investigated the mechanics of a concentric solid tube (CST) model in which motion is generated by expanding and contracting actuator rings pushing and pulling the membrane around a solid inner tube. In this paper, we present the mechanics of a fluid filled toroid (FFT) model which replaces the solid inner tube with incompressible fluid. Locomotion using contracting ring actuation is described for the FFT model and compared to the CST model. A novel actuation scheme which exploits the chemo-mechanics of soft polymeric elastic skin is also introduced to elicit useful locomotive behavior. Chemically induced swelling in polymeric skin is demonstrated to be a viable propulsion mechanism for a toroidal membrane under pressure. Finally, preliminary analysis is presented for finding forces required for a WSL robot to squeeze through a hole of a given depth and diameter to investigate the feasibility of using contracting ring actuation and chemically induced swelling for hole traversal.
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